A disc drive is a data handling system used to store digital data. A typical disc drive includes a number of rotatable magnetic recording discs which are axially aligned and mounted to a spindle motor for rotation at a high constant velocity. A corresponding array of read/write heads are supported by a rotary actuator and used to access fixed sized data blocks (sectors) on tracks of the discs to write data to and to read data from the discs.
Digital data to be written to the disc recording surfaces are encoded and serialized to provide a sequence of time-varying write currents to the heads. The write currents induce a corresponding sequence of magnetic flux transitions (reversals) along the tracks. The data are subsequently read by transducing the magnetic flux transitions into pulses of an analog readback signal, which is subjected to decoding techniques to recover the originally written digital data. Disc drives of the present generation typically employ sampled amplitude read channels with discrete time sequence detection.
It is common to perform media certification tests to scan the disc surfaces for media defects during disc drive assembly operations. Broadly speaking, media defects are regions in the magnetic medium of the disc surfaces where data cannot be reliably written and retrieved. A number of factors can induce media defects including minute pinholes, asperities, contaminants, etc. induced in the discs during disc manufacturing.
With the continuing trend of providing ever increasing areal data storage densities on the disc recording surfaces, it is becoming increasingly difficult to produce discs with no media defects, and it is cost prohibitive to only use flawless discs and discard (scrap) discs containing such defects. Hence, disc drive manufacturers typically implement schemes to locate and map media defects so that such locations are subsequently avoided in the writing of user data. During a formatting operation in which the data sectors are defined on the disc surfaces, the disc drive will map out sectors that coincide with the location of the detected media defects so that data are not written to defective sectors.
At the same time, as areal data storage densities increase, the amount of time required to scan the disc recording surfaces for defects increases; not only in terms of the additional amounts of data that must be written and read back from the disc surfaces, but also in terms of the time required to process the test results and generate a defect list. There is a need, therefore, for improvements in the art whereby media certification can be performed in a disc drive data handling system in an efficient and reliable manner.